The present invention is directed to a method for deodorizing sulfur-containing solvents and to ink compositions containing the deodorized solvent. More specifically, the present invention is directed to a process for deodorizing sulfur-containing solvents with an oxidizing agent to convert odor-causing impurities therein to compounds with reduced or no objectionable odor. One embodiment of the present invention is directed to a process which comprises contacting a sulfur-containing solvent with an oxidizing agent, said sulfur-containing solvent containing odor-causing impurities, thereby reducing odor. Another embodiment of the present invention is directed to a process for preparing an ink composition which comprises: (a) contacting a sulfur-containing solvent with on oxidizing agent, said sulfur-containing solvent containing odor-causing impurities, thereby reducing odor; and (b) admixing the sulfur-containing solvent with water and a colorant, thereby forming an ink composition.
Ink jet printing systems generally are of two types: continuous stream and drop-on-demand. In continuous stream ink jet systems, ink is emitted in a continuous stream under pressure through at least one orifice or nozzle. The stream is perturbed, causing it to break up into droplets at a fixed distance from the orifice. At the break-up point, the droplets are charged in accordance with digital data signals and passed through an electrostatic field which adjusts the trajectory of each droplet in order to direct it to a gutter for recirculation or a specific location on a recording medium. In drop-on-demand systems, a droplet is expelled from an orifice directly to a position on a recording medium in accordance with digital data signals. A droplet is not formed or expelled unless it is to be placed on the recording medium.
Since drop-on-demand systems require no ink recovery, charging, or deflection, the system is much simpler than the continuous stream type. There are two types of drop-on-demand ink jet systems. One type of drop-on-demand system has as its major components an ink filled channel or passageway having a nozzle on one end and a piezoelectric transducer near the other end to produce pressure pulses. The relatively large size of the transducer prevents close spacing of the nozzles, and physical limitations of the transducer result in low ink drop velocity. Low drop velocity seriously diminishes tolerances for drop velocity variation and directionality, thus impacting the system's ability to produce high quality copies. Drop-on-demand systems which use piezoelectric devices to expel the droplets also suffer the disadvantage of a slow printing speed.
The other type of drop-on-demand system is known as thermal ink jet, or bubble jet, and produces high velocity droplets and allows very close spacing of nozzles. The major components of this type of drop-on-demand system are an ink filled channel having a nozzle on one end and a heat generating resistor near the nozzle. Printing signals representing digital information originate an electric current pulse in a resistive layer within each ink passageway near the orifice or nozzle, causing the ink in the immediate vicinity to evaporate almost instantaneously and create a bubble. The ink at the orifice is forced out as a propelled droplet as the bubble expands. When the hydrodynamic motion of the ink stops, the process is ready to start all over again. With the introduction of a droplet ejection system based upon thermally generated bubbles, commonly referred to as the "bubble jet" system, the drop-on-demand ink jet printers provide simpler, lower cost devices than their continuous stream counterparts, and yet have substantially the same high speed printing capability.
The operating sequence of the bubble jet system begins with a current pulse through the resistive layer in the ink filled channel, the resistive layer being in close proximity to the orifice or nozzle for that channel. Heat is transferred from the resistor to the ink. The ink becomes superheated far above its normal boiling point, and for water based ink, finally reaches the critical temperature for bubble formation or nucleation of around 280.degree. C. Once nucleated, the bubble or water vapor thermally isolates the ink from the heater and no further heat can be applied to the ink. This bubble expands until all the heat stored in the ink in excess of the normal boiling point diffuses away or is used to convert liquid to vapor, which removes heat due to heat of vaporization. The expansion of the bubble forces a droplet of ink out of the nozzle, and once the excess heat is removed, the bubble collapses on the resistor. At this point, the resistor is no longer being heated because the current pulse has passed and, concurrently with the bubble collapse, the droplet is propelled at a high rate of speed in a direction towards a recording medium. The resistive layer encounters a severe cavitational force by the collapse of the bubble, which tends to erode it. Subsequently, the ink channel refills by capillary action. This entire bubble formation and collapse sequence occurs in about 10 microseconds. The channel can be refired after 100 to 500 microseconds minimum dwell time to enable the channel to be refilled and to enable the dynamic refilling factors to become somewhat dampened. Thermal ink jet processes are well known and are described in, for example, U.S. Pat. No. 4,601,777, U.S. Pat. No. 4,251,824, U.S. Pat. No. 4,410,899, U.S. Pat. No. 4,412,224, and U.S. Pat. No. 4,532,530, the disclosures of each of which are totally incorporated herein by reference.
Japanese Patent Publication JP-4103673, the disclosure of which is totally incorporated herein by reference, discloses a water-based ink for ink jet recording containing water, an aqueous dye, and a water soluble organic solvent, further containing as a deodorizer a benzotriazole derivative compound of the formula ##STR1## wherein each of R.sub.1 and R.sub.2 are hydrogen, hydroxy, or alkyl groups with 1 to 12 carbon atoms, and X is hydrogen or halogen. The deodorizer removes odor from organic solvents, such as glycol ethers and DMSO.
In some water miscible solvents desirable for use in aqueous ink jet inks, particularly those containing sulfur (such as sulfolane), very low concentrations of unoxidized sulfur-containing compounds can impart a very disagreeable odor to the solvent, even at the parts per million and parts per billion levels. Sulfolane is a polar, aprotic solvent that has found use in a wide variety of ink jet ink formulations. Its high boiling point makes it act as a humectant, and it also imparts some level of penetration to inks. For use in ink jet inks, this solvent must undergo extensive purification because of odor and, at times, color associated with impurities often found in the material. Even after extensive purification, certain impurities at the parts per billion level in the solvent can still result in significant odor. In addition, these impurities are less soluble in water than pure sulfolane, so that when the solvent is admixed with water to make the ink, the impurities have a greater tendency to vaporize, thereby accentuating the odor. Known purification methods include extensive distillation followed by passing the material through carbon bed filters, and the like; distillation alone is not sufficient to remove these impurities. These methods are expensive, take long periods of time, generate a substantial amount of waste, and do not enable uniform results; even after use of these purification methods, unacceptable odor can still remain. Other sulfur-containing solvents, such as alkyl sulfoxides or alkyl sulfones, can exhibit similar problems.
Accordingly, while known materials and methods are suitable for their intended purposes, a need remains for improved methods for deodorizing sulfur-containing solvents. In addition, a need remains for improved ink compositions suitable for use in thermal ink jet printers. Further, a need remains for methods for treating impurities in sulfur-containing solvents which enable reduction or elimination of undesirable odor from the treated material. Additionally, a need remains for methods for deodorizing sulfur-containing solvents which are cost effective. There is also a need for methods for deodorizing sulfur-containing solvents which can be employed prior to admixing the sulfur-containing solvents with other ink components. In addition, there is a need for methods for deodorizing sulfur-containing solvents which can be employed with an ink composition containing sulfur-containing solvents and other ink ingredients. Further, there is a need for methods for deodorizing sulfur-containing solvents which also disinfect the ink. Additionally, there is a need for methods for oxidizing common impurities in sulfur-containing solvents which cause an undesirable odor and/or, wherein the oxidized forms of the impurities exhibit little or no undesirable odor and/or color. A need also remains for ink compositions containing materials which, when incorporated into thermal ink jet ink compositions containing sulfur-containing solvents, oxidize impurities which cause an undesirable odor and/or color, thereby converting the impurities to a form having little or no undesirable odor and/or color, and which also impart to the ink composition antibacterial properties.